Fault‐controlled dolomite bodies as palaeotectonic indicators and geofluid reservoirs: New insights from Gargano Promontory outcrops          下载免费PDF全文

Andrea Rustichelli  Alessandro Iannace  Emanuele Tondi  Claudio Di Celma  Antonino Cilona  Maurizio Giorgioni  Mariano Parente  Monica Girundo  Chiara Invernizzi 《Sedimentology》2017,64(7):1871-1900

The Upper Jurassic to Lower Cretaceous platform‐slope to basinal carbonate strata cropping out in Gargano Promontory (southern Italy) are partly dolomitized. Fieldwork and laboratory analyses (petrographic, petrophysical and geochemical) allowed the characterization of the dolomite bodies with respect to their distribution within the carbonate succession, their dimensions, geometries, textural variability, chemical stability, age, porosity, genetic mechanisms and relation with tectonics. The dolomite bodies range from metres to kilometres in size, are fault‐related and fracture‐related, and probably formed during the Early Cretaceous at <500 m burial depths and temperatures <50°C. The proposed dolomitization model relies on mobilization of Early Cretaceous seawater that flowed, downward and then upward, along faults and fractures and was modified in its isotopic composition moving through Triassic and Jurassic strata that underlie the studied dolomitized succession. Despite the numerous cases reported in literature, this study demonstrates that hydrothermal and/or high‐temperature fluids are not necessarily required for fault‐controlled dolomitization. Distribution and geometries of dolomite bodies can be used for palaeotectonic reconstructions, as they partly record the characteristics (size, attitude and kinematics) of the palaeo‐faults, even if not preserved, that controlled dolomitization. In Gargano Promontory, dolomites record Early Cretaceous palaeo‐faults from metres to kilometres long, striking north‐west/south‐east to east/west and characterized by normal to strike‐slip kinematics. Dolomitization increases the matrix porosity by up to 7% and, therefore, can improve the geofluid storage capacity of tight, platform‐slope to basinal limestones. The results have a great significance for characterization of geofluid (for example, hydrocarbons) reservoirs hosted in similar dolomitized carbonate successions. Distribution, size and shapes of reservoir rocks (i.e. dolomite bodies) could be broadly predictable if the characteristics of the palaeo‐fault system present at the time of dolomitization are known.  相似文献   

Large-Scale Temperature Changes across the Southern Andes: 20th-Century Variations in the Context of the Past 400 Years   总被引：4，自引：0，他引：4  

Ricardo Villalba  Antonio Lara  José A. Boninsegna  Mariano Masiokas  Silvia Delgado  Juan C. Aravena  Fidel A. Roig  Andrea Schmelter  Alexia Wolodarsky  Alberto Ripalta 《Climatic change》2003,59(1-2):177-232

Long-term trends of temperature variations across the southern Andes (37–55° S) are examined using a combination of instrumental and tree-ring records. A critical appraisal of surface air temperature from station records is presented for southern South America during the 20th century. For the interval 1930–1990, three major patterns in temperature trends are identified. Stations along the Pacific coast between 37 and 43° S are characterized by negative trends in mean annual temperature with a marked cooling period from 1950 to the mid-1970s. A clear warming trend is observed in the southern stations (south of 46°S), which intensifies at higher latitudes. No temperature trends are detected for the stations on the Atlantic coast north of 45° S. In contrast to higher latitudes in the Northern Hemisphere where annual changes in temperature are dominated by winter trends, both positive and negative trends in southern South America are due to mostly changes in summer (December to February) temperatures. Changes in the Pacific Decadal Oscillation (PDO) around 1976 are felt in summer temperatures at most stations in the Pacific domain, starting a period with increased temperature across the southern Andes and at higher latitudes.Tree-ring records from upper-treeline were used to reconstruct past temperature fluctuations for the two dominant patterns over the southern Andes. These reconstructions extend back to 1640 and are based on composite tree-ring chronologies that were processed to retain as much low-frequency variance as possible. The resulting reconstructions for the northern and southern sectors of the southern Andes explain 55% and 45% ofthe temperature variance over the interval 1930–1989, respectively. Cross-spectral analysis of actual and reconstructed temperatures over the common interval 1930–1989, indicates that most of the explained varianceis at periods >10 years in length. At periods >15 years, the squaredcoherency between actual and reconstructed temperatures ranges between 0.6 and 0.95 for both reconstructions. Consequently, these reconstructions are especially useful for studying multi-decennial temperature variations in the South American sector of the Southern Hemisphere over the past 360 years. As a result, it is possible to show that the temperatures during the 20thcentury have been anomalously warm across the southern Andes. The mean annual temperatures for the northern and southern sectors during the interval 1900–1990 are 0.53 °C and 0.86 °C above the1640–1899 means, respectively. These findings placed the current warming in a longer historical perspective, and add new support for the existence of unprecedented 20th century warming over much of the globe. The rate of temperature increase from 1850 to 1920 was the highest over the past 360 years, a common feature observed in several proxy records from higher latitudes in the Northern Hemisphere.Local temperature regimes are affected by changes in planetary circulation, with in turn are linked to global sea surface temperature (SST) anomalies. Therefore, we explored how temperature variations in the southern Andes since 1856 are related to large-scale SSTs on the South Pacific and South Atlantic Oceans. Spatial correlation patterns between the reconstructions and SSTs show that temperature variations in the northern sector of the southern Andes are strongly connected with SST anomalies in the tropical and subtropical Pacific. This spatial correlation pattern resembles the spatial signature of the PDO mode of SST variability over the South Pacific and is connected with the Pacific-South American (PSA) atmospheric pattern in the Southern Hemisphere. In contrast, temperature variations in the southern sector of the southern Andes are significantly correlated with SST anomalies over most of the South Atlantic, and in less degree, over the subtropical Pacific. This spatial correlation field regressed against SST resembles the `Global Warming' mode of SST variability, which in turn, is linked to the leading mode of circulation in the Southern Hemisphere. Certainly, part of the temperature signal present in the reconstructions can be expressed as a linear combination of four orthogonal modes of SST variability. Rotated empirical orthogonal function analysis, performed on SST across the South Pacific and South Atlantic Oceans, indicate that four discrete modes of SST variability explain a third, approximately, of total variance in temperature fluctuations across the southern Andes.  相似文献   

Trends of Extreme Temperatures in Europe and China Based on Daily Observations   总被引：15，自引：0，他引：15  

Z. Yan  P. D. Jones  T. D. Davies  A. Moberg  H. Bergström  D. Camuffo  C. Cocheo  M. Maugeri  G. R. Demarée  T. Verhoeve  E. Thoen  M. Barriendos  R. Rodríguez  J. Martín-Vide  C. Yang 《Climatic change》2002,53(1-3):355-392

Ten of the longest daily temperature series presently available in Europe and China are analysed, focusing on changes in extremes since pre-industrial times. We consider extremes in both a relative (with respect to the time of year) and an absolute sense. To distinguish changes in extremes from changes affecting the main part of the temperature distribution, a percentile smaller than 10 (and/or larger than 90) is recommended for defining an extreme. Three periods of changes in temperature extremes are identified: decreasing warm extremes before the late 19th century; decreasing cold extremes since then and increasing warm extremes since the 1960s. The early decreases and recent increases of warm extremes dominate in summer, while the decrease of cold extremes for winter persists throughout the whole period. There were more frequent combined (warm plus cold) extremes during the 18th century and the recent warming period since 1961 at most of the ten stations, especially for summer. Since 1961, the annual frequency of cold extremes has decreased by about 7% per century with warm extremes increasing by more than 10% per century but with large spatial variability. Compared with recent annual mean warming of about 2–3 ° C/century, the coldest winter temperatures have increased atthree times this rate, causing a reduced within-season range and therefore less variable winters. Changes in the warmest summer temperatures since 1961 exhibit large spatial variability, with rates of change ranging from slightly negative to 6 ° C/century. More extensive station observations since 1961 indicate that the single site results are representative of larger regions, implying also that the extremes studied are the result of large-scale changes. Recent circulation changes in daily gridded pressure data, used as an indicator of wind speed changes, support the results by explaining some of the trends.  相似文献   

Geomorphological evidence of the influence of pre-volcanic basement structure on emplacement and deformation of volcanic edifices at the Cofre de Perote–Pico de Orizaba chain and implications for avalanche generation     

Aline Concha-Dimas  Mariano Cerca  Sergio R. Rodríguez  Robert J. Watters   《Geomorphology》2005,72(1-4):19-39

Pre-volcanic structure of the basement influences volcanism distribution and avalanche generation in volcanic edifices. Therefore, systematic studies of basement structure below volcanic chains are necessary to understand the deformation effects observed in the surface and vice versa. Based on a compilation of pre-existing data, interpretation of aerial photographs and satellite images, and a collection of structural data we analyzed morphological and structural features of the Cofre de Perote–Pico de Orizaba (CP–PO) volcanic chain and its basement. We have identified three sets of regional lineaments that are related to basement trends. (1) NW 55° SE fractures are parallel to anticline folds observed in Cretaceous rocks that originated during Laramide shortening. These folds present an abrupt morphology observed only in the eastern flank but that is likely to continue below the volcanic chain. (2) NE 55° SW fractures are parallel to normal faults at the basement. We infer that these basement faults confine the CP–PO chain within a stepped graben with a total normal displacement of about 400 m. These faults have been active through time since they have affected volcanic deposits and induced the emplacement of monogenetic vents. Notably, lineaments of monogenetic vents concentrate where the basement is relatively shallow. (3) Another set of faults, oriented N–S, has been observed affecting the scarce basement outcrops at the western flank of the chain covered by lacustrine deposits. Lineaments measured in the volcanic edifice of Pico de Orizaba correlate with the regional trends.In particular, the NE 55° SW alignment of monogenetic vents and fractures at Pico de Orizaba suggest that the same dike trend exists within the volcanic edifice. A normal fault with similar orientation was documented at the NE continuation of an alignment crossing the volcanic edifice along the Jamapa canyon. In the absence of magmatic activity related to collapses, the displacement of NE 55° SW faults represents a potential triggering mechanism for generating avalanches at Pico de Orizaba volcano. Instability is enhanced by the presence of N–S trending fractures crossing the entire volcanic edifice and E–W fractures affecting only the present day cone. We conclude that mechanical instability of the volcanic chain is influenced by the basement structure heterogeneity, but further detailed studies are necessary at individual volcanoes to evaluate their effects on volcano deformation.  相似文献   

In situ Permeability Measurements Based on a Radial Gas Advection Model: Relationships Between Soil Permeability and Diffuse CO2 Degassing in Volcanic Areas     

Marco Camarda  Sergio Gurrieri  Mariano Valenza 《Pure and Applied Geophysics》2006,163(4):897-914

In this paper we have developed a new method for measuring in situ soil permeability, which is based on the theory of radial gas advection through an isotropic porous medium. The method was tested in the laboratory and at several locations on the island of Vulcano (Aeolian Islands, Italy). It consists of a special device which generates a gas source at a depth of 50 cm and it permits measurement of the relative induced pressure in nearby soil at different depths. The characteristic error of the method was less than 10%. Furthermore, soil permeability measurements were carried out in the island of Vulcano during different periods of the year (between May 2000 and June 2001). A strong decrease in permeability in the upper layers of the soil during and after rainfall was noted, with very poor correlations between the spatial distributions of soil CO₂ flux and shallow soil permeability.  相似文献   

3-D density model of Mt. Etna Volcano (Southern Italy)     

Domenico Schiavone  Mariano Loddo 《Journal of Volcanology and Geothermal Research》2007

A detailed density model of Mt. Etna and its surrounding areas has been evaluated using a 3-D inversion of the gravimetric data acquired in the 1980's. Several high-density and low-density bodies are found, penetrating from shallow depths as far down as 12 km bsl. A positive correlation (in terms of location, extent, density, and velocity) is established between several anomalies of the density model and features identified in previously published seismic tomographies. A prominent high-density body extending down to 7 km bsl is recognized in the southern part of the Valle del Bove, and interpreted as a solidified magmatic intrusion. On the western boundary of this anomaly, a low-density body is interpreted as a bubble and liquid magma mixture. Outside the central area, three other high-density anomalies are imaged and attributed to the earliest phases of volcanic activity in the area. Several interesting low-density anomalies are also identified and correlated with known fault lines and other structural features of the region.  相似文献   

全球中期模式升级关键技术研发和预报试验     

陈起英  管成功  姚明明  佟华  Mariano Hortal  李泽椿 《气象学报》2007,65(4):478-492

随着模式分辨率的提高,对地形、海陆分布的描述更加精确,从而对天气和次天气尺度动力学的刻画也更准确,但计算需求和存贮量也将有比较明显的增加。因此,在模式分辨率提高的同时尽可能减少计算和存储量是模式发展的重要方面。文中采用规约线性格点,在高斯格点数和格点分布不变的情况下,把国家气象中心业务全球谱模式的水平分辨率由T213提高到TL319,从而使全球谱模式的计算有效率增加了2.25倍;实现了稳定外插两个时间层的半拉格朗日方案,解决了传统的半拉格朗日方案在计算轨迹中点的速度和发展方程的非线性项时,采用时间的线性外插带来的计算噪音,提高了模式积分的稳定性,从而使模式的积分时间步长从900 s增加到1200 s;在这两个关键技术实现的基础上,实现了TL319模式与业务OI同化方案的耦合,进行了连续1年的滚动试验,并对降水预报和500 hPa形势场预报进行了统计学检验,与现行全球中期业务模式的预报也进行了对比分析。分析结果表明,提高模式谱分辨率后,模式的动力过程保持合理稳定,对东亚地区500 hPa位势高度场的预报性能有所改进,对中雨和大雨量级的降水预报在大部分时效也都有改进,但是小雨预报TS评分略有下降。另外对冬、夏季的两次降水过程的天气学分析表明,TL319L31对天气过程的描绘比T213L31也有一定提高。  相似文献   

On the tectonics of the Neocomian Rio do Peixe Rift Basin, NE Brazil: Lessons from gravity, magnetics, and radiometric data     

David Lopes de Castro  Digenes Custdio de Oliveira  Raimundo Mariano Gomes Castelo Branco 《Journal of South American Earth Sciences》2007,24(2-4):184-202

A geophysical perspective based on well-acquired gravity, magnetic, and radiometric data provides good insights into the basin architectural elements and tectonic evolution of the Rio do Peixe Basin (RPB), an Early Cretaceous intracontinental basin in the northeast Brazilian rift system, which developed during the opening of the South Atlantic. NW–SE-trending extensional forces acting over an intensively deformed Precambrian basement yielded a composite basin architecture strongly controlled by preexisting, mechanically weak fault zones in the upper crust. Reactivated NE–SW and E–W ductile shear zones of Brasiliano age (0.6 Ga) divided the RPB into three asymmetrical half-grabens (Brejo das Freiras, Sousa, and Pombal subbasins), separated by basement highs of granite bodies that seem to anchor and distinguish the mechanical subsidence of the subbasins. Radiometric and geopotential field data highlight the relationship between the tectonic stress field and the role of a preexisting structural framework inserted in the final rift geometry. The up-to-2000 m thick half-grabens are sequentially located at the inflexion of sigmoidal-shaped shear zones and acquire a typical NE–SW-oriented elliptic shape. The Sousa Subbasin is the single exception. Because of its uncommon E–W elongated form, three-dimensional gravity modeling reveals an E–W axis of depocenters within the Sousa Subbasin framework, in which the eastern shoulders are controlled by NE–SW-trending faults. These faults belong to the Precambrian structural fabric, as is well illustrated by the gamma ray and magnetic signatures of the basement grain. Release faults were identified nearly perpendicular or oblique to master faults, forming marginal strike ramps and horst structures in all subbasins. The emplacement mechanism of Brasiliano granites around the RPB was partially oriented by the same structural framework, as is indicated by the gravity signature of the granitic bodies after removal of the gravity effect of the basin-filling deposits. The RPB major-fault occurrence along the releasing bend of a strong discontinuity – the so-called Portalegre Shear Zone – in addition to the configuration of a gentle crustal thinning, according to gravity field studies, suggests that a crustal discontinuity governs the nucleation of the RPB, followed probably by small displacement in deep crustal levels accommodating low-rate stretching during basin subsidence.  相似文献   

Nummulitids,lepidocyclinids and Sr-isotope data from the Oligocene of Kutch (western India) with chronostratigraphic and paleobiogeographic evaluations     

György Less  Gianluca Frijia  Ercan Özcan  Pratul K. Saraswati  Mariano Parente  Pramod Kumar 《Geodinamica Acta》2018,30(1):183-211

Due to its intermediate geographical position between the Mediterranean and W Pacific, the Oligocene shallow-marine sequence of Kutch (India) is of key importance in paleobiogeographical interpretations. Larger benthic foraminifera (LBF) are a fundamental link for the correlation between the Mediterranean shallow benthic zones (SBZ) and the W Pacific ‘letter stages’. LBF were re-evaluated by morphometric studies of the internal test from five stratigraphic sections of the Maniyara Fort Formation. Based on their significant affinity to coeval fauna in the Mediterranean, they were assigned to W Tethyan SBZ zones, supported by Sr-isotope stratigraphy. In the Basal Member, traditionally considered as early Rupelian, we identified Nummulites bormidiensis, N. kecskemetii and Heterostegina assilinoides assigning it to the early Chattian SBZ 22B Zone. The Coral Limestone Member, previously considered as late Rupelian, is also assigned to this zone, for the presence of N. bormidiensis, Eulepidina formosoides-dilatata and Nephrolepidina morgani-praemarginata. Its early Chattian age (26.5–29 Ma) is further supported by Sr-isotope data. Miogypsinoides complanatus and Spiroclypeus margaritatus in the Bermoti Member (the top of the formation) document the late Chattian SBZ 23 Zone and the Sr-isotope data (22.5–24 Ma) place it close to the Oligocene–Miocene boundary.  相似文献   

Genetic heterogeneity in populations of the Mediterranean shore crab, Carcinus aestuarii (Decapoda,Portunidae), from the Venice Lagoon     

Ilaria Anna Maria Marino  Federica Barbisan  Micol Gennari  Folco Giomi  Mariano Beltramini  Paolo Maria Bisol  Lorenzo Zane 《Estuarine, Coastal and Shelf Science》2010

Heterogeneity in genetic composition among recruits, mostly due to a large variance in reproductive success mediated by oceanographic processes, has been reported for marine species but is less understood in coastal lagoons' organisms. Temporal genetic variation in natural populations of the Mediterranean shore crab Carcinus aestuarii was quantified over a multi-year sample. A total of 486 adult crabs were collected at eight different sites of the Venice Lagoon during the period 2005–2007 and screened for genetic variation using 11 microsatellite loci. Two additional samples (N = 115) from neighbouring sites, located approximately 100 km North and South to the Venice Lagoon, were included for the sake of comparison. Our results show significant differences in allelic frequencies at the micro-geographic scale of the Venice Lagoon, observed between sites of collection, typologies of habitat, and areas with different class of ecological risk or pattern of hemocyanin expression. However, this pattern was not constant between years, with significant differences observed mainly in 2005 and 2006, but not in 2007. Our results indicate significant temporal differences suggesting the existence of dynamic processes that act on the genetic pool of this species. Although natural selection and gene flow might play a role, we suggest that genetic drift linked to large variation in the reproductive success of individuals is the most probable scenario to explain the local genetic patterns of differentiation in the Mediterranean shore crab. Our study, by providing the first evidence for the existence of genetic differences in this species at the micro-geographic scale, suggests that a better comprehension of the link between reproduction, recruitment and oceanography is critical to understand how colonization and maintenance of genetic variation is achieved in ephemeral and vulnerable environments such as coastal lagoons.  相似文献